Galactic AGB stars from the IPHAS survey
N.J. Wright, M.J. Barlow, R. Greimel, J.E. Drew, M. Matsuura
aa r X i v : . [ a s t r o - ph . S R ] D ec The Galactic Plane, in depth and across the spectrumXXVIIth IAU General Assembly, August 2009Janet Drew and Melvin Hoare, eds c (cid:13) Galactic AGB stars from the IPHAS survey
N.J. Wright, M.J. Barlow, R. Greimel, J.E. Drew and M. Matsuura Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 University College London, Gower Street, London WC1E 6BT, U.K. Institut f¨ur Physik, Karl-Franzen Universit¨at Graz, Universit¨atsplatz 5, 8010 Graz, Austria University of Hertfordshire, College Lane, Hatfield, AL10 9AB, U.K.
Abstract.
Asymptotic giant branch (AGB) stars are one of the final evolutionary stages of all interme-diate mass stars and one of the major sources of enriched material returned to the interstellarmedium, including all s-process elements and the majority of carbon. Quantitative knowledge oftheir chemistries and mass-loss rates is therefore vital for an understanding of galactic chemicalevolution. The INT Photometric H α Survey (IPHAS, Drew et al. 2005) is imaging the entirenorthern Galactic plane using Sloan r ′ , i ′ , and narrow-band H α filters. The use of broad-bandfilters in the red makes this survey excellent at highlighting AGB stars whose cool photospheresemit predominantly in the red and near-IR. Additionally, one of the unique features of theIPHAS colour-colour diagram is that the main-sequence and giant branches are well separatedat late spectral types, effectively allowing the AGB population across the entire northern Galac-tic plane to be identified and studied. Wright et al. (2008) presented a photometric analysis ofthe most extremely reddened sources in the IPHAS colour-colour diagram and confirmed thatthey were predominantly late-type AGB stars with high levels of circumstellar material thatcontributed to their reddening.Follow-up spectroscopy on a number of optical and near-IR instruments has allowed thispopulation to be studied in more detail. Wright et al. (2009) published a near-IR spectral libraryof AGB stars with a particular focus on very late-type sources. The spectral library includesspectra in all three near-IR bands as well as many variables objects and chemically evolvedsources such as S-type and carbon stars. The library includes spectral classification sequenceshighlighting the various molecular features identified and discusses a number of rare features,for which the potential molecules responsible are discussed.Finally we discuss a correlation between the IPHAS ( r ′ − H α ) colour and the C/O abundanceindex (Keenan & Boeshaar, 1980). Wright et al. (2009) found that the IPHAS ( r ′ − H α ) colourcould be used to estimate C/O ratios for S-type stars and therefore determine their state ofchemical evolution in the transition from O-rich (C/O <
1) to carbon rich (C/O >
1) via theintermediate S-type phase (C/O ∼ Keywords. stars: AGB and post-AGB - stars: chemically peculiar - stars: carbon - infrared:stars - atlases - techniques: spectroscopic
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